There are several categories of prior art which constitute the relevant background to the invention.
The first category of prior art is concerned with switches comprising only one displaceable beam steering arrangement facing a plurality of fixed output ports. Many examples of this category of switches exist, for example: U.S. Pat. No. 6,335,993B1(Takahashi) where the single mobile collimator is fixed to a disk rotating about a central axis; U.S. Pat. No. 4,896,935(Lee) where a single displaceable collimator is rotatable to point towards a series of radially extending collimators; and U.S. Pat. No. 657,339(Fick) where a single displaceable fibre through a contraction of a one-dimensional piezo electric arrangement allows the fibre to bend in between two positions where fixed fibres are located. Other examples in this category may be structures with a single fixed input port and multiple fixed output ports with a single optical element displaced to achieve switching such as JP2004287124(Nin Sensho) and CA2002386309(Sun De-Gui).
Further examples with a single displaceable beam steering arrangement are shown in US2003/0072520(Wu et al); JP58072108(Matsui); and U.S. Pat. No. 5,436,986(Tsai). EP0496224A2 may also be included in this category since it shows a single two part optical switch whose lenses are displaced through the action of a single actuator. The displacement of the lenses occurs simultaneously with the displacement of the displaceable beam steering arrangement.
A second category of prior art exists which shows multiple input and output switches with a number of actuators equaling the total number of ports. In other words, these often require the input and the output ports to be displaceable for switching to occur. WO01/50176 (Polatis), U.S. Pat. No. 6,256,429 (Ehrfeld et al), WO02/43432 (Arol) and U.S. Pat. No. 6,005,998 (Lee) show at least one actuator per port. In other words, for a total of M+N ports there are provided at least M+N actuators to displace optical elements. U.S. Pat. No. 6,859,120 (Sweatt William et al) also shows a system using actuators on both the input and output side of an optical switch.
A third category of switches relies on the use of at least two displaceable optical elements between fixed arrays of input and output ports. For example, U.S. Pat. No. 6,456,751B1(Bowers et al) shows the use of two micro-actuated arrays of mirrors. Another example can be found in JP2001350105 where a series of at least two movable prisms is envisaged to switch a beam from one port to another in a multiple input and multiple output switch. This category of switches also requires at least the same number of actuated optical elements as their total number of ports.
A fourth category of switches uses the same number of input or output ports as the number of beam steering arrangements of the switch. US2002/0003919(Morimoto) has the same number of tiltable optical beam steering arrangements as the number of input ports. It fails however to transmit an entire beam from an input port to an output port since the inputs broadcast a fan across all the mirrors which results in large losses. The optical beam steering arrangements therefore fail to substantially intercept entire beams originating from input ports and to subsequently direct a beam on a path to an output port. Furthermore, the displaceable arrangements of the prior art also fail to displace to and from positions of interception of substantially entire beams. They simply are rotatable on the spot with no displacement to and from a location where individual interception may be achieved.